Phosphorus Pools Associated with Fish in the Archipelago Sea

This study compiled and updated data for constructing the phosphorus budget of the Archipelago Sea, with a particular focus on estimating the size of phosphorus pools associated with fish populations. Biomass data and species-specific phosphorus content were used, and a bioenergetic modeling approach was applied to Baltic herring (Clupea harengus membras) and European perch (Perca fluviatilis) to estimate species-specific food consumption and nutrient excretion. Between 2001 and 2024, average total phosphorus concentrations were 28% higher than during the baseline period of 1983–1989. From 1998 to 2023, the annual average fish catch in the Archipelago Sea was 15,516.5 tons (16.3 kg/ha), of which 73.1% consisted of commercially harvested herring. The annual catch contained, on average, 83.4 tons of phosphorus. Fishing may have removed annually phosphorus equivalent to approximately 0.6% of the total phosphorus pool in the water column and surface sediment, or 1.4% of the estimated total phosphorus load of the Archipelago Sea. The contribution of fish to phosphorus turnover is minor; phosphorus recycling is dominated by plankton. Planktivorous fish and their prey recycle nutrients already present in the water column and are therefore not the root cause of eutrophication.